1. Field of the Invention
This invention relates to an instrument probe assembly and, in particular, to a probe assembly useful for capacitance measurement detection of process variables such as liquid levels and the like.
2. Brief Statement of the Prior Art
Instrument probes such as elongated metal rods, often coated with a dielectric material, are commonly used for measurement of process variables such as the level of a liquid or granular solid within a containing vessel. The elongated probes have a metal core which is received within an assembly body that usually has a threaded gland portion and the like which is received within a nozzle or aperture of a pressure vessel. The probe member is secured within the assembly body and protected against dislodgement thererfrom by an annular retainer ring mounted in a peripheral groove in the portion of the probe member within the assembly body. Spacer ring of dielectric material are positioned on opposite faces of the retainer ring and the entire retainer portion of the probe member is encased within dielectric sleeves which are mounted within a cavity of the assembly body. While this construction adequately retains the probe member within the assembly, process fluids can invade the assembly body and destroy the electrical isolation of the probe member metal core. Additionally, the aforementioned construction employs a number of components which must be assembled, thereby contributing to a substantial intial cost of the assembly.